1) what are the two main functions of a datagram-based network layer? what additional functions does a vc-based network layer have? 2) list and describe the atm network service models. 3) compare and contrast link-state and distance-vector routing algorithms. 4) discuss how a hierarchical organization of the internet has to scale to millions of users. 5) it is necessary that every autonomous system use the same intra-autonomous routing algorithm? why or why not?